Lubricating oil in an internal combustion engine is used to lubricate engine components to reduce wear, seizing, and overheating, thereby extending the life of the engine. Lubricating oil may be pumped from an oil sump of the engine through passageways to various components of the head of the engine (e.g., camshaft bearings, lash adjusters, and variable cam timing components) and throughout the engine (e.g., to main bearings, pistons, the crankshaft, etc.). Gravity then pulls the oil back down to the oil pan through oil drain-back passages. The oil drains from the engine head through the oil drain-back passages to replenish the oil within the oil pan which is continuously pumped throughout the engine via a high pressure oil circuit.
However, the inventors herein have recognized potential issues with such systems. As one example, at high engine speeds, large pressure fluctuations driven by the translation of the pistons, rotation and translation of the connecting rods, and the rotation of the crankshaft occur in the crankcase. The dominant flow mechanism is produced by the translational motion of the pistons. This phenomenon is commonly known as crankcase pumping and is attributed to power losses, as well as inhibiting the flow of oil down the oil drain-backs. As a result, at high engine speeds, oil may accumulate in the cylinder head and not drain down to the oil sump. Further, the oil pump will not replenish oil throughout the engine if the oil is unable to drain to the oil sump, thereby leading to insufficient oil circulation and potential wear of components in the engine.
In one example, the issues described above may be addressed by an engine (e.g., an internal combustion engine) comprising: a cylinder block including a plurality of cylinders, each cylinder including a piston disposed therein; a crankcase including a plurality a bulkhead walls separating pistons of the plurality of cylinders, where at least one bulkhead wall includes a crankcase breathing window disposed therein and fluidly coupling two adjacent crankcase bays; and an oil drain-back passage including an entrance into the crankcase at the crankcase breathing window. As one example, the crankcase breathing window may be a passage arranged between the two adjacent crankcase bays, through the at least one bulkhead wall separating the two adjacent crankcase bays. The breathing window may create a localized constriction through which a fluid's velocity increases and the fluid's pressure reduces, thereby causing a Venturi effect. By directing the oil-drain passage into the crankcase via the crankcase breathing window, the low pressure caused by the Venturi effect during engine operation creates a suction and downward flow of oil from the cylinder head, thereby leading to more oil drain-back into the oil sump. Thus, oil circulation through the engine may be increased.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.